This invention relates to an apparatus and method for removal of sludge from tanks and more particularly to such an apparatus and method which utilizes a floating roof or cover in the tank over the liquid in which the sludge is formed.
Heretofore, such as shown in U.S. Pat. No. 4,364,776, dated Dec. 21, 1982, various methods or processes have been utilized for the removal of a body of sludge formed in storage tanks for crude or partly refined oil. Such methods have included the circulation of solvents to dissolve or disperse the sludge within the oil, but such methods have normally recirculated the lighter sludge fraction and dispersed chemicals from positions adjacent the sides of the tanks generally in a swirling action. By recirculation from the side of the tank, only a relatively small portion of the total fluid volume within the relatively large tank is recirculated and oftentimes, the main body of sludge is located at or adjacent the center of the tank and not the side of the tank. Such recirculation methods and systems heretofore have not utilized the mixing energy efficiently since a major energy output is utilized in obtaining a relatively high flow velocity adjacent the side of the tank, but not employed in circulating the contents of the tank to any extent adjacent the center portion of the tank. Thus, previous methods and apparatus have required relatively large periods of time for the dispersal and removal of the sludge from an associated tank, such as a week for example, during which the fluids were circulated continuously for twenty-four (24) hours each day.
The aforesaid U.S. Pat. No. 4,364,776 attempted to solve this problem of the recirculating fluid reaching the main body of sludge by utilizing lances inserted within the sludge from the side of the tank. However, it is noted that oil tanks containing sludge have a diameter from around fifty (50) feet to around three hundred (300) feet and it is difficult to utilize lances effectively from the side of the tank, particularly when large diameter tanks such as two hundred (200) feet or more in diameter are involved. Further, when only one lance for each pump is provided, only a relatively small portion of the sludge is reached by the recirculating liquid and thus requires considerable time in which to disperse the sludge.